In recent years, with improvement of wireless communication networks including mobile telephone networks, service has become widespread that provides content to a terminal apparatus which is mounted and used on a mobile unit such as a car. It is preferable that the content to provide to the terminal apparatus mounted on a mobile unit is content related to positions through which the mobile unit passes.
For example, a technique called “LOCATIONWARE” is known, as a conventional technique to present to a terminal apparatus the content related to a position which a mobile unit passes through. “LOCATIONWARE” is described in Documents 1 and 2 as described below.
Document 1: Sakata, et al. “A Proposed “Location-aware Notification Service” Information Processing Society Japan, SIG Technical Reports on Mobile Computing and Wireless Communication, 2000-MBL-15-10, Vol.2000, No.112, pages 78–80, December, 2000.
Document 2: Kurashima, et al. “Technologies for Notification Service in Location-aware Service Platform “LOCATIONWARE”, NEC Technical Report, Vol.54, No.7, 2001.
In the technique, a server receives a current position and maximum cache amount of a terminal apparatus from the terminal apparatus. The server sets an acquisition range (cache range) in the vicinity of the received position of the terminal apparatus, and retrieves information (content) related to a position in the acquisition range from a position-related information database. The acquisition range is set so that the total amount of content data in the acquisition range is within the maximum cache amount.
The server transmits the retrieved content data and information of the acquisition range to the terminal apparatus. Thus, the content related to the current position is presented to a user of the terminal apparatus.
Communications between a server and terminal in the conventional technique will be described below with reference to FIG. 1. FIG. 1 illustrates communications between the server and terminal apparatus in the conventional technique.
In time period B1, terminal apparatus 1702 transmits position information of terminal apparatus 1702 to server 1701. Next, in time period B2, server 1701 calculates an acquisition range based on the received position information, and retrieves content data associated with the calculated acquisition range. In time period B3, server 1701 transmits information of the acquisition range to terminal apparatus 1702. In time period B4, server 1701 transmits the content data to terminal apparatus 1702.
It is necessary to present content related to a position at suitable timing to a terminal apparatus mounted on a mobile unit whose position moves with the passage of time.
When content related to a position is presented after a mobile unit has passed through the position, the presented content does not related to a position of the terminal apparatus, and has little value.
Further, when loads on the server are large due to concentrated access on the server, it takes a time for the server to retrieve content data. Therefore, in the conventional technique as disclosed in the above-mentioned documents, it happens that the mobile unit has moved during a period of time the server retrieves the content data, and the content is not presented to the terminal apparatus at appropriate timing.
Timing relating to communications between server 1701 and terminal apparatus 1702 will be described below specifically with reference to FIG. 2. FIG. 2 shows timing relating to communications between server 1701 and terminal apparatus 1702 in the conventional technique.
Time axis 1710 shows timing relating to communications between server 1701 and terminal apparatus 1702 in the case where access is not concentrated on the server.
In this case, terminal apparatus 1702 starts transmission (B1) of position information to server 1701 at time t=0, and server 1701 completes transmission (B4) of content data to terminal apparatus 1702 before time 1705.
Time 1705 is the time desired to display the content data to terminal apparatus 1702, and for example, the time the mobile unit mounted with the terminal apparatus passes through the position in relation to the content data.
In the timing indicated on time axis 1710, it is possible to display the content data to terminal apparatus 1702 appropriately.
Time axis 1711 shows timing relating to communications between server 1701 and terminal apparatus 1702 in the case were access is concentrated on the server.
In this case, terminal apparatus 1702 starts transmission (B1) of position information to server 1701 at time t=0, and server 1701 completes transmission (B4) of content data to terminal apparatus 1702 after time 1705.
In the timing indicated on time axis 1711, transmission of content data to terminal apparatus 1702 is not completed at time 1705. Therefore, it is not possible to present the content data to terminal apparatus 1702 at appropriate timing.
This is because concentrated access on server 1701 increases time required for server 1701 to calculate an acquisition range and retrieve contend data by time 1704.
In particular, when a mobile unit mounted with a terminal apparatus moves at high speed, a possibility is high that content data is not presented at appropriate timing due to the fact that the time increases required for server 1701 to calculate an acquisition range and retrieve the contend data.